1. Field of the Invention
The present invention relates to an image signal process system which processes an image in the form of electrical signals.
2. Description of the Prior Art
There are already proposed various image processings in which an image is converted into electrical signals for transmission, storage etc.
A binary representation of an A3-sized image with a resolving power of 400 dpi requires image signals of ca. 4 Mbytes, thus requiring a memory of the same capacity for the storage of said signals.
The use of image compression is therefore proposed. Such compression can generally reduce the amount of data of image to about 1/10, thus allowing the use of a relatively small memory.
In a case of extracting, for example for image formation, a part of the image represented by the compressed and stored image signals, such extraction is conducted after the compressed image signals are expanded. However such expansion requires complex operations which take a considerable time and may generate errors requiring certain error recovery processes. However, such error recovery process is wasteful if such error belongs to a part of the image not selected for extraction.
Also in case of moving the image represented by the compressed and stored image signals or forming a moved image by extracting a portion of said image, synchronization with an image forming apparatus is difficult to achieve.
Also, in a case of extracting a part of the input image signals for image formation or transmission, the compression of image signals corresponding to an unnecessary image area or the storage of such image signals is not only unnecessary but also gives rise to a higher probability of errors in compression, resulting from compression of such unnecessary image signals.
Also, it may be required to synthesize an image compressed and stored in the above-explained manner with another image for example for image formation, but exact registration of two images is difficult to achieve.
Also, in a case of an image formation by overlaying plural images through synthesis of plural image signals respectively representing different images, the synthesized image may show unpleasant local differences in image density, if the densities of the images to be synthesized, represented by respective electrical image signals, are significantly different. On the other hand, if plural images to be overlaid have the same density, one image may be masked by an other image. Also, it is not possible to independently regulate the densities of the images, for example for reproducing a background image with a low density and characters with a high density.